Usually, it is known to insert the steel monopile into a ground, with a driving hammer for instance.
Next, a connecting element made of concrete is poured on top of the steel monopile on which the precast concrete part is disposed to connect the steel monopile and the precast concrete part.
The connecting element is generally equipped with a reinforcement cage.
When several piles are arranged such that a pile cap extends on all the piles, there are larger room tolerances for positioning the pile cap and/or for positioning the precast concrete part on top of it relatively to the piles showing construction errors. The positioning can easily be achieved by minor adjustments on the pile cap reinforcement cage so that the tolerance in position of the concrete upper parts is not affected.
However, when only one monopile is used with its associated concrete part, for instance for an offshore wind turbine, there is needed matching diameters between the monopile and the associated concrete part and the geometrical tolerances are more restricted.
For instance, for a steel monopile diameter of 2.5 m, a horizontal tolerance is approximately 50 mm while a vertical tolerance is approximately 75 mm.
Nevertheless, such restricted tolerances are more difficult to work with because of the absence of the pile cap to adapt the piles construction errors. Adjustment capacities are then required to cope with construction errors of the monopile for horizontal position, height or tilt angle. Furthermore, the need for adjustment capacity should favorably have a limited impact on the duration of the whole construction process of a superstructure bearing onto the foundation.